CAMTASIA 9. FIRST INSTALL OK. THE REINSTALL DOES NOT GO THROUGH BECAUSE OF THE SERIAL KEY

I have purchased months ago cumtasia 9 through camtasia store.The install went well. I have beeen using the soft since then.I came accross a problem so I have uninstalled the software but after attemptingthe reinstallation I get an error message and the key I enter is not acccepted.A person from the support tried to fix the problem directly entering my PC with no luck.Can anyone came accross such a problem.Thanks for your help.